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1 29 March 2004 . AGE-NC Project No. 97-0327 Page 10 of 12 Typically, ground water would represent the migration medium for contaminants over significant ' horizontal distances; however, sites located in an up-gradient direction from the site are not likely to be negatively impacted. In addition,first encountered ground water is not used for drinking water or irrigation, although all ground water in the State of California is considered to be of potential beneficial use. ' Based upon laboratory analysis of ground water samples collected beneath the site, the zone of maximum petroleum hydrocarbon-impacted ground water appeared to be located near soil boring yP-8 and the southwest cor�ne the former UST pit area;the plume extends laterally approximately 60 feet towards the nsehea"s "but is poorly defined in all other directions (Figure 11). The vertical SIJ extent of the hydrocarbon-impacted ground water plume appears to be greater than 70 feet bsg; its maximum vertical extent is not well defined in all directions. r Drinking water at and near the site is supplied by municipal wells, although private wells were identified in the year 2000 search of well drillers reports at the CDWR. Thirty private water wells ' were identified within a 2,000-foot radius of the site; the nearest private wells were located approximately 700 feet toward the southwest (Appendix ' 8.0. SUMMARY AND CONCLUSIONS ' The key components of the site conceptual model include: The subsurface soil stratigraphy generally consists of a/ery stiff to hard,fine grained sandy ' SILT at depths between 10 feet and 25 feet bsg,between 40 feet and 50 feet bsg and between 60 feet and 65 feet bsg; a medium dense to dense, silty fine sand was generally encountered at depths between 25 feet and 40 feet bsg, 50 feet and 60 feet bsg and at depths greater than 65 feet bsg. • Based on the subsurface soil distribution,AGE informally identified vadose-zone petroleum- impacted soil to be located between surface grade and 45,feet bsg, smear-zone petroleum- impacted soil to be located between 45 feet and 62 feet bsg, and any saturated-zone petroleum-impacted soil to be located at depths greater than 62 feet bsg. ' 0 . Vm r`- 7-OS The lateral extent of petroleum-impacted soil-appears to be moderately defined beneath the former UST area and towards the northwest and southeast where gasoline- and diesel- impacted soil appears to be limited;however, there is uncertainty towards the southwest at --depths between 30'and`40 feet bsg`and-towards the northeast at depths between 35 and,45Y- --- feet bsg-(Figures 5 through 8)where the soil-impacted plume may extend laterally beneath. Fremont Street and Oro Avenue. The vertical extent of gasoline-and diesel-impacted soil is ' moderately defined beneath the former UST area and in all directions where gasoline- and diesel-impacted soil does not appear to extend beyond.50 feet bsg (Figures 5 through 8). 55 r 1